Temporary Superintendent Emma Bond branded the incident a "despicable act". She highlighted that many houses and two primary schools are situated close to where the device was found and said there could have been multiple casualties if a mortar had been launched.

"Those who are behind this attack had very clear and I believe murderous intent," she said. "This is a very reckless attack."

The suspected mortar and launcher were found on waste ground at the foot of Black Mountain in north-west Belfast around 500 metres to the rear of the police station at 7.15am. An off-duty police officer on the way to work and a passing taxi driver both reported the suspicious items.

Many houses lie between the site and the perimeter of the station.

Ms Bond said a clear line of inquiry was that the mortar was targeted at the PSNI facility.

She said police believe it was placed some time between last night and early Friday morning and was likely transported to the scene in a vehicle.

"Initial indications and my opinion are at this stage is that had this device successfully gone ahead or exploded then it would have had deadly and fatal consequences for an innocent member of the public, a member of the police service or anybody else," she said.

Two primary schools were forced to close and a funeral was disrupted by the security alert. Many residents remained out of their homes while the operation to make the area safe continued.